Good day!
Yes, missions can be done in advance.
You can, in principle, open the shooting area in advance, and scroll through it so that the maps are saved in the cache. Then it will be possible to create a mission at the shooting location and not miss the area. Before entering an unconnected area, be sure to connect to the drone and check for updates. I had a situation when I didn't check it, drove 150 km into the wilderness, as a result, the Mavic Mini did not allow me to take a normal shot, there was a limitation on the height (up to 30 meters) and on the distance (up to 50 meters), which is very inconvenient.
Good luck to you!